The present invention relates to a vehicle headlight with a dirt sensor for a diffuser disk, this sensor receiving the light of a lamp, such as an incandescent lamp, scattered back due to dirt on the diffuser disk and being shielded against the light emanating directly from this lamp and emanating indirectly via a reflector.
A headlight of this type has been known, see DOS [German Unexamined Laid-Open Application] No. 2,137,231, the sensor of which receives directly the light reflected on the dirt on the diffuser disk. In this known headlight the sensor is arranged in the interior of the headlight, especially within a bore of the reflector. However, such an arrangement is disadvantageous in that the bore impairs the optical properties of the reflector and thus of the headlight, on the one hand, by a possible alteration in the parabolic configuration of the reflector during and after production of the bore and, on the other hand, by a reduction of the effective surface area for light emission. Furthermore, sealing problems can occur with such an arrangement in the case of hermetically sealed headlights such as sealed beam headlights.
Thus, an object of the present invention is to overcome the aforementioned disadvantages of the known headlight with dirt sensor and, specifically, to arrange, in a vehicle headlight of the type described hereinabove, the dirt sensor without changes to the reflector and without reduction of the effective surface area of the reflector.
This and other objects of the present invention are attained according to the present invention by arranging the sensor at a point outside of the reflector, the back-scattered light being transmitted to this point via reflection on the reflector.
The light scattered by the dirt on the diffuser disk passes, in part, indirectly via reflection on the reflector into the sensor. Therefore, the reflector, on the one hand, aligns the light of the headlight lamp and, on the other hand, reflects the light scattered on the dirt into the sensor.
According to one form of the present invention the dirt sensor can be arranged on the inside of the diffuser disk. Alternatively, the sensor can be mounted in an airtight fashion on the outer surface of the diffuser disk in which case it is possible to attach the sensor subsequent to the manufacture of the headlight. Such attachment can be carried out on an installed headlight and does not require any alteration of the latter.
An especially advantageous arrangement of the dirt sensor according to the present invention, in a headlight emitting a low beam from one of its halves, resides in arranging the sensor in the other, "dark" half. The sensor in this case is located in a zone into which falls no light from the headlight lamp, either directly or by reflection on the reflector. A special shielding of this light can in this case be omitted.
According to the present invention the sensor can also be arranged at the rim of the diffuser disk. In such an arrangement the sensor does not impair the optical properties of the headlight and cannot be discerned from the outside. If it is additionally located in the "dark" half of a low-beam headlight, then the high-beam light normally emitted from this headlight is not impaired in any way, either.
The sensor can furthermore be aligned with or oriented toward a zone of the reflector located laterally with respect to the plane determined by the axis of the headlight and the position of the sensor. In such a case, essentially only such light passes into the sensor which is reflected from dirt on the diffuser disk, so that a shielding of the light from the headlight lamp, emitted either directly or indirectly, is extensively eliminated. Furthermore, due to such alignment or orientation of the sensor, an impairment of the light stemming from the dirt accumulation by a parabolic bulb reflector customary in headlights for directly emitted light from the headlight lamp is avoided.